Michael Hayden, a former director of the NSA and the CIA, on Friday called Russia’s interference in the 2016 presidential election the “most successful covert influence operation in history.”

“Frankly, [the Russian meddling] is the most successful covert operation in history,” Hayden told a national security panel in response to a question from moderator Yahoo News Chief Investigative Correspondent Michael Isikoff. Hayden said the original cyberattack on the Democratic National Committee was not that surprising — and even from an intelligence perspective, impressive.

“I just have to admit as a former director of NSA, [Russia’s hack and theft of email] is honorable state espionage,” Hayden said to audience laughter, speaking at the Aspen Security Conference.

Isikoff interjected, asking if the Russian dissemination of the emails through WikiLeaks should still be considered “honorable state espionage.”

“If we as NSA could have an insight into … Russia through the same techniques, game on,” Hayden said. “But now you make the great distinction: What the Russians then did with the information. And then that turned [it] into what we call a covert influence operation.”

Hayden argued that the release of stolen Democratic emails on WikiLeaks was the Kremlin’s egregious act, not the hacks to obtain the information.

“This is, at its heart, not a cyber issue. At its heart, this is a Russia issue,” Hayden said. “The cyber-thing was a preliminary action in order to get some raw materials, … but that’s not what made this different. That’s not what made this egregious.”

Isikoff asked why the U.S. government has yet to clearly delineate a “red line” when it comes to cybersecurity violations from other countries even though the cyberthreat has existed for years.

Former Homeland Security Secretary Michael Chertoff, also on the panel, responded that the Defense Department had issued a guideline which said attacks warrant a response if they result in loss of life or serious economic damage.

“The truth is the technology and the techniques that can be used have actually evolved more rapidly than our thinking about it,” Chertoff said. “The value of norms would be it would start to create a basis for law-abiding countries to know when they can respond to a cyber act as if it were an act of war.”

The U.S. lacks a standard of proof, which makes it difficult to prove who’s responsible for a cyber attack, Chertoff said.

“If we confront the Russians, their response is, ‘Well, you don’t have 100 percent proof, so we reject it,’” Chertoff said. “We have to establish a consensus about how much is enough.”

Isikoff then pivoted to discuss the Syrian refugee crisis, which he said has resulted in 4.9 million refugees in Lebanon, Jordan and Turkey, noting that former FBI agent Ali Soufan called it “the greatest humanitarian disaster of our lifetime.”

National Counterterrorism Center Director Nick Rasmussen, another panel participant, said he wouldn’t want to draw “a straight line” connection between someone being displaced by the Syrian civil war and that person becoming a potential recruit for terrorists.

But Rasmussen said that Soufan’s description still holds. “First and foremost, it’s a humanitarian crisis of epic proportions, but it does have a long-term security piece to it that we’re going to be managing for a number of years,” he said.

The counterterrorism expert also said the Lebanese militant group Hezbollah poses a threat to the U.S. The Iranian-backed organization is recognized by the intelligence community as one of the most capable terrorist groups in the world, with access to technology and state sponsorship, he said.

But FBI arrests of individuals with ties to Hezbollah in the U.S. suggests that there’s a presence of Hezbollah operatives in the homeland, Rasmussen said.

“We’ve known they look to lay infrastructure in all parts of the world to give itself options, to develop a playbook,” Rasmussen said.

A bipartisan group of lawmakers introduced legislation in the House and Senate on Thursday that would increase sanctions on Hezbollah for its actions in Syria and near the Israeli border.